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Predicting effects of climate change on blue crabs in Chesapeake Bay.
Hines, AH; Johnson, EG; Darnell, MZ; Rittschof, D; Miller, TJ; Bauer, LJ; Rodgers, P; Aguilar, R
Callinectes sapidus populations support fisheries extending over a broad range of latitude from the species’ tropical origins into the temperate zone. We analyzed latitudinal patterns of survival, reproduction, growth and maturation of blue crab populations in Florida, North Carolina, and Maryland/Virginia to project demographic effects of climate warming and certain other potential climate changes on the Chesapeake blue crab population. Field surveys and laboratory experiments indicate that harsh winters (<3ºC, <8 ppt salinity) cause significant mortality in small (10 mm) juveniles and mature females. Brooding in populations at lower latitudes begins 3-4 months earlier than at high latitudes, allowing more broods per season. Cold winter temperature also restricts the growing season and inserts a prolonged period of suspended activity compared to lower latitudes, where juveniles grow rapidly to mature in one season rather than two at higher latitudes. However, tethering experiments indicate predation and cannibalism on juveniles is muchhigher during the warm season than spring and fall. Although there are not clear trends across latitude, size at maturity is inversely correlated with temperature within a site. While small females may molt to maturity and mate sooner, small size increases vulnerability to predation and diminishes fecundity per brood. Thus, cold winter temperatures and a short growing and reproducing season restrict the species’ northward distribution from its tropical origins. Climate change reducing the severity of winters is predicted to increase winter survival and to promote rapid growth and brood production. However, warmer temperatures may promote increased juvenile mortality and may reduce size at maturity. Demographic schedules for fishery models will need to consider complex effects of warming.
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